In 1937 he joined the Radical Party, and under the government of Juan Antonio Ríos, in 1942, he was appointed general director of the Ministry of Economy and Commerce.

[2] In 1948 he became the first president of the United Nations Economic Commission for Latin America and the Caribbean (CEPAL), and led Chile's delegations to the conferences of this organization in Havana (1949), Montevideo (1950), and Mexico (1951).

Baltra, who had been on the left wing of the Radical Party and was president of the Chilean-Soviet Culture Institute, resisted the course his political group was taking during the Allende government.

Finally – along with other well-known politicians such as Luis Bossay [es] – he ended up renouncing it on 3 August 1971 and, the same day, forming the Independent Left Radical Movement.

For the parliamentary elections of March 1973, the PIR joined with other center-right opposition parties in the Confederation of Democracy, formed in July 1972, and Baltra ran for Senator for Santiago, but received only 1.92% of the vote.

[1] Alberto Baltra died on 20 September 1981, the victim of a cardiac arrest while walking down Antonio Varas Street near his house in the district of Providencia.